func_get_annotation_dict missing critical section after gh-128714 #159091

Bug report

gh-128714 added @critical_section to the __annotations__ setter and deleter, but the getter (function___annotations___get_impl) and its helper func_get_annotation_dict were not protected.

// NO @critical_section on the getter
static PyObject *
function___annotations___get_impl(PyFunctionObject *self)
{
    ...
    d = func_get_annotation_dict(self);  // reads + Py_XSETREF without lock
}

// line ~976 — setter has @critical_section, getter does not

func_get_annotation_dict (line 539) does an unprotected read of op->func_annotations and a Py_XSETREF into it at line 557. A concurrent setter holds a critical section; the getter does not. This is a read-write race.

Found while auditing CPython with cpython-review-toolkit (maintained by @devdanzin and myself).

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-159091: Fix a data race in PyFunction_GetAnnotations() #159094